It is often desirable to modify the thermal properties of plastics, such that the resultant plastic is more suitable for certain applications that include thermal stresses. Such additives may have uses in industries where it is desirable to have plastic materials with greater thermal conductivity, such as plastic components for solar and geothermal energy systems, plastic automotive parts, and high heat output lighting system components. Thermally conductive materials may also be used in non-thermoplastic technologies such as coatings for automotive and industrial applications as well as in electrical storage systems where thermal management is a consideration.
One example application is improving the thermal conductivity of plastics used as coverings for automotive headlights. Due to their intense brightness, the bulbs used in automotive headlights can generate large amounts of heat which could damage surrounding components. By increasing the thermal conductivity of the plastic covering, the plastic is better able to dissipate the heat generated by the headlight.
Another example application is blow molding, a typical manufacturing process by which hollow plastic parts, such as bottles and other containers, are formed. In blow molding, a plastic parison or preform is heated until softened. Once softened, air is blown into the parison or preform to push the plastic against a mold. Once the plastic has cooled, the mold is opened and the plastic part is removed. Typical plastics used for food packaging include polypropylene and polyethylene terephthalate (collectively, “the plastics”). Due to the relatively poor ability of the plastics to absorb infrared radiation, the process of heating the plastic typically limits the rate at which a blow molding process can produce bottles. Heating the plastics to the desired temperature also requires large amounts of energy, increasing the cost of the manufacturing process. Accordingly, it is common to add additives to the plastic resins in order to include the rate at improve the heat-up rate.
Common additives include finely dispersed inert black materials, such as carbon black having a mean particle diameter of at least 200 nanometers (nm) as disclosed by European Patent No. 1,809,690 to Harrison et al., that absorb the energy emitted by infrared energy sources used in blow molding machines. Carbon black is a form of paracrystalline carbon typically produced by the incomplete combustion of heavy petroleum products. However, a need still exists for additives that improve the thermal properties of plastics beyond the capabilities of known additives such as carbon black.